Category: 04. The circle

In this lesson, we show what inscribed and circumscribed circles are using a triangle and a square. Circles can be placed inside a polygon or outside a polygon.  Inscribed circles When a circle is placed inside a polygon, we say that the circle is inscribed in the polygon. Two examples of circles inscribed in a…

Concentric circles are coplanar circles that share the same center. However, radii of concentric circles are not congruent or equal. Concentric circle The circles above are examples of concentric circles. Notice that the radius of the smaller circle is shown in black while the radius of the big circle is shown in red.  The region…

Tangent circles are coplanar circles that intersect in exactly one point. They can be externally tangent or internally tangent. Circles that are tangent internally Circles that are tangent internally have one circle inside the other. In the image below, you can clearly see that the smaller circle is located inside the bigger circle. Furthermore, both circles…

Approximating the area of a circle using what we know about the area of a square is the method we are going to use here. Our technique is to inscribe a circle inside a square as shown below: Then, inscribe a square inside the circle. Draw two diameters and they are shown in black Label…

The area of a circle is the space taken by the circle in a two-dimensional plane. In the figure below, notice that the space occupied or taken by the circle on the left is less. Therefore, the area of the smaller circle on the left is less. Area of circle formula The most common way…

The four different ways to find the radius of a circle are shown below: How to find the radius of a circle using the diameter In a circle, the radius is always half the length of its diameter. r = d / 2 Example #1: Find the radius if the diameter is 20 inches r…

The circumference of a circle, also called the perimeter of a circle, is the distance around a circle or any circular object such as a clock, a pizza, or a dinner plate. For example, the distance around a circular clock is the circumference of the clock.  How to find the circumference of a circle? Method…

The number pi (π) is equal to 3.14159265 seven places after the decimal point. It is commonly used when calculating the circumference and the area of a circle, which formulas are equal to 2 × π × r and π × r2 respectively. An experiment or activity you can do at home that will show you…

What is a circle? In geometry, a circle is the locus of points located at the same distance from a given fixed point.  The word locus sounds complicated, but it means set of all points on a plane. The fixed point is called center of the circle. Another way then to define a circle is…